In February 2019, as amended in July 2019, we entered into a Series A financing transaction, pursuant to which we were authorized to issue up to 18,992,220 shares of Series A redeemable convertible preferred stock having a per share par value of $0.0001, at a purchase price of $3.4225 per share.

The terms of the Series A redeemable convertible preferred stock agreement include provisions requiring the investors to purchase, and obligating us to deliver, additional shares of redeemable convertible preferred stock at a specified price in the future based on the achievement of certain development-based milestones by us. The investors are also able to waive the milestone requirements, which provides the investors with an option to purchase additional Series A redeemable convertible preferred stock if the milestone is not met. The rights to purchase additional shares were recorded as a tranche liability at the estimated fair value of the obligation on the date of issuance with the carrying values adjusted at each reporting date for any changes in the estimated fair values. For the three and nine months ended September 30, 2020, we recorded $8.4 million and $9.5 million, respectively, for the change in the fair value of the redeemable convertible preferred stock tranche liability.

Upon closing of the Merger, the outstanding redeemable convertible preferred stock tranche rights terminated and all redeemable convertible preferred stock that had been issued converted to common stock.

We have a total of five operating leases as of September 30, 2021 with remaining lease terms of approximately 3 months to 9 years.

In June 2021, we entered into a sublease agreement for office space in Seattle, Washington (“Seattle Sublease”), which we expect to use as our corporate headquarters. The Seattle Sublease commenced on July 1, 2021 and continues for a period of 58 months. The aggregate estimated base rent payments due over the remaining term of the Seattle Sublease is approximately $5.5 million.

As of September 30, 2021, we are subleasing approximately 110,000 square feet in one of our facilities. Sublease income was $1.7 million and $0 for the three months ended September 30, 2021 and 2020, respectively, which was netted against rent expense. Sublease income was $4.4 million and $0 for the nine months ended September 30, 2021 and 2020, respectively, which was netted against rent expense. Total sublease income to be earned, in aggregate, will be approximately $67.6 million over the remaining term of the sublease agreement.

We maintain a letter of credit as security for one of our leases in the amount of $1.8 million, which is collateralized by a certificate of deposit that is included in restricted cash in our Condensed Consolidated Balance Sheet as of September 30, 2021. Additionally, in connection with the Seattle Sublease, we posted a security deposit of $0.3 million in the form of a letter of credit, which was collateralized by a certificate of deposit and is included in restricted cash in our Condensed Consolidated Balance Sheet as of September 30, 2021.

The maturity of our operating lease liabilities as of September 30, 2021 is as follows (in thousands):

Undiscounted Lease Payments	Amounts
2021 (remaining three months)	$	1,778
2022		7,483
2023		7,695
2024		7,850
2025		8,009
Thereafter		26,079
Total undiscounted lease payments		58,894
Present value adjustment		13,937
Total net lease liability	$	44,957
Net lease liability – current	$	4,194
Net lease liability - non-current		40,763
Total net lease liability	$	44,957

Rent expense recognized for operating leases was $2.4 million and $0.1 million for the three months ended September 30, 2021 and 2020, respectively, and was $6.4 million and $0.4 million for the nine months ended September 30, 2021 and 2020, respectively. Variable lease payments, including non-lease components such as common area maintenance fees, recognized as rent expense for operating leases were $0.5 million and less than $0.1 million for the three months ended September 30, 2021 and 2020, respectively, and were $1.7 million and $0.2 million for the nine months ended September 30, 2021 and 2020, respectively.

	September 30, 2021	December 31, 2020
Weighted-average remaining lease terms (in years)
Operating leases	7.7		8.8
Weighted-average discount rate
Operating leases	7.5%	7.1%

In the ordinary course of business, we enter into agreements that may include indemnification provisions. Pursuant to such agreements, we may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments we could be required to make under these provisions is not determinable. We have never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. We have also entered into indemnification agreements with its directors and officers that require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. We currently maintain directors’ and officers’ liability insurance.

From time to time, we may become involved in litigation relating to claims arising from the ordinary course of business. Management believes that there are no actions pending against us currently, the ultimate disposition of which would have a material adverse effect on our results of operations, financial condition or cash flows.

We have various manufacturing, clinical, research and other contracts with vendors in the conduct of the normal course of its business. All contracts are terminable, with varying provisions regarding termination. If a contract with a specific vendor were to be terminated, we would only be obligated for the products or services that we had received at the time the termination became effective as well as non-cancelable and non-refundable obligations, including payment obligations for costs or expenses incurred by the vendor for products or services before the termination became effective. In the case of terminating a clinical trial agreement at a particular

site, we would also be obligated to provide continued support for appropriate medical procedures at that site until completion or termination.